Structure and crystallizability of K2O-B2O3-SiO2 and K2O-B2O3-GeO2 glasses: Effect of composition and heat treatment mode

The stability and crystallizability of glasses K2O-B2O3-GeO2 and K2O-B2O3-SiO2 systems becomes an important consideration when selecting materials for optical purposes and the immobilization of radioactive wastes. To determine the crystallizability of boron-containing glasses, thermal treatments were carried out at 500 and 680 degrees C and the formed phases were identified. The structural features of the materials before and after treatment were studied by vibration spectroscopy. Glasses with B2O3/SiO2 = 2/5 and B2O3/GeO2 = 4/3 ratio proved to be the most resistant to heating. It was observed that the ratio of B/Si and B/Ge has a significant effect on crys-tallizability at any temperature. Heat treatment at 680 degrees C results in the formation of potassium borates, silicates, and borosilicates in the borosilicate system, while the crystallization of germanates and potassium borates is characteristic of the borogermanate system. Structural differences between the crystallization products of these two systems are shown to be due to the ability of germanium to form highly oriented structural units. With an increase in the B/Ge ratio, the crystallization of borogermanate glasses is shown to lead to a decrease in the proportion of crystalline borates. Conversely, during the crystallization of the borosilicate system, an increase in the B/Si ratio in the initial glass leads to an increase in their content.